brachium

Borrowed from Latin bracchium (“arm”). Doublet of braccio.

brachium (plural brachia or brachiums)

1. (anatomy) The upper arm.

• aftarm (rare, nonstandard)

Probably secondary, via the common substitution of /VC:/ for /V:C/, the inverse of the littera rule (as in Iuppiter).

• (Classical Latin) IPA^(key): [ˈbraː.kʰi.ũː]
• (modern Italianate Ecclesiastical) IPA^(key): [ˈbraː.ki.um]

brāchium n (genitive brāchiī or brāchī); second declension

1. alternative form of bracchium (“arm”)

Second-declension noun (neuter).

¹Found in older Latin (until the Augustan Age).

• brachium in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
• "brachium", in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)